Transparent electrode and method for fabricating the same, and electronic device using the transparent electrode

Abstract

[Problem] Provided are: a transparent electrode that can be manufactured at a low temperature, that has a low sheet resistance, that is highly transparent, and with which a lightweight, flexible solar cell, large-area illumination, etc. are realized; a manufacturing method therefor; and an electronic device employing the aforementioned transparent electrode. [Solution] A transparent electrode according to an embodiment has a silver nanowire network. This transparent electrode has a silver nanowire in which a minimum radius of curvature r of a curve is equal to or less than 2 μm and a bending angle θ is equal to or greater than 90° and contains a compound that has a boiling point of 160°C or lower and that has an alkynyl group and a hydroxyl group.

Description

[Technical Field]

[0001] Embodiments of the present invention relate to transparent electrodes, methods for manufacturing the same, and electronic devices. [Background technology]

[0002] In recent years, energy consumption has been increasing, and the demand for alternative energy sources to replace conventional fossil fuels is growing as a measure against global warming. Solar cells are attracting attention as one such alternative energy source, and their development is progressing. Solar cells are being considered for various applications, but flexibility and durability are particularly important to accommodate diverse installation locations. The most basic monocrystalline silicon solar cells are expensive and difficult to make flexible, while organic solar cells and organic-inorganic hybrid solar cells, which have recently attracted attention, have room for improvement in terms of durability.

[0003] In addition to solar cells, studies are being conducted on photoelectric conversion elements such as organic EL elements and light sensors, with the aim of making them more flexible and improving their durability. ITO films are typically used as transparent electrodes in these elements. ITO films are usually fabricated by sputtering. Achieving high conductivity requires high-temperature sputtering or high-temperature annealing after sputtering, which is often not applicable to organic materials.

[0004] In contrast, silver nanowires are attracting attention as a new type of transparent electrode because they can be coated and deposited at low temperatures. However, further improvements are needed in terms of light transmittance and conductivity. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2013 / 151142 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] In view of the above-mentioned problems, this embodiment provides a transparent electrode that can be manufactured at low temperatures, has low sheet resistance, is highly transparent and lightweight, and enables the production of flexible solar cells and large-area lighting, as well as a method for manufacturing the same, and an electronic device using the transparent electrode. [Means for solving the problem]

[0007] The transparent electrode according to the embodiment is a transparent electrode having a network of silver nanowires, wherein the network includes silver nanowires whose minimum radius of curvature r of the curve is 2 μm or less and whose bending angle Θ is 90° or more.

[0008] Another transparent electrode according to this embodiment is a transparent electrode having a network of silver nanowires, further comprising a compound having a boiling point of 160°C or less and having an alkynyl group and a hydroxyl group.

[0009] The method for manufacturing a transparent electrode according to the embodiment is: (A) A step of producing a dispersion containing silver nanowires and a compound having an alkynyl group and a hydroxyl group. (B) A step of applying the dispersion onto a substrate, and (C) Process of heating and drying the substrate after coating. It possesses the following characteristics.

[0010] Furthermore, the electronic element according to this embodiment comprises the transparent electrode, a photoelectric conversion layer, and a counter electrode on a transparent substrate. [Brief explanation of the drawing]

[0011] [Figure 1] Conceptual diagram of silver nanowires according to an embodiment. [Figure 2] Conceptual diagram of a transparent electrode according to the first embodiment. [Figure 3] Conceptual diagram of the transparent electrode configuration according to the second embodiment. [Figure 4] Conceptual diagram of a method for manufacturing a transparent electrode according to an embodiment. [Figure 5] Conceptual diagram showing the structure of a photoelectric conversion element (solar cell) according to an embodiment. [Figure 6] Conceptual diagram showing the structure of a photoelectric conversion element (organic EL element) according to an embodiment. [Figure 7] SEM photograph of the surface of the transparent electrode of Example 1. [Figure 8] SEM cross-sectional photograph of the transparent electrode of Example 1. [Figure 9] SEM photograph of the surface of the transparent electrode of Comparative Example 1. [Figure 10] SEM cross-sectional photograph of the transparent electrode of Comparative Example 1. [Figure 11] Conceptual diagram showing the structure of a photoelectric conversion element (solar cell) of Example 3. [Figure 12] Conceptual diagram showing the structure of a photoelectric conversion element (solar cell) of Example 4.

BEST MODE FOR CARRYING OUT THE INVENTION

[0012] Hereinafter, embodiments will be described in detail.

[0013] [Embodiment 1] First, the configuration of the transparent electrode according to the first embodiment will be described using FIGS. 1 and 2. The transparent electrode according to the embodiment has a network of silver nanowires. Silver nanowires are generally linear, but the transparent electrode according to the embodiment is characterized in that it contains silver nanowires having bends. And, due to the silver nanowires having bends, it exhibits excellent characteristics different from those of the conventional transparent electrodes composed of silver nanowires.

[0014] FIG. 1 is a conceptual diagram showing the bending angle and minimum radius of curvature of the silver nanowire 10 according to the present embodiment. When the silver nanowire has a bend, its shape may have a three-dimensional shape, but in the embodiment, only two-dimensional shapes are considered. That is, when the silver nanowire has a three-dimensional shape, its shape is examined using a projection view seen from one direction.

[0015] The bending angle Θ of a silver nanowire is defined as follows. First, we assume a current vector 11 at a point in the silver nanowire 10 when a current flows in a constant direction. Then, we determine the vector 11 at all points in the silver nanowire. The maximum value of the angle between the vector directions of any two of these points is defined as the bending angle Θ. Therefore, the bending angle Θ of a straight silver nanowire with no bending is zero. Also, the bending angle Θ will never exceed 180°.

[0016] Furthermore, the minimum radius of curvature of the silver nanowire is defined as the radius of curvature at the point where the rate of change in the direction of the vector at each point is greatest, as determined above.

[0017] Figure 2(A) is a conceptual diagram of a network 22 containing only silver nanowires with very small bending angles. This conceptual diagram shows how current I flows from left to right. Such silver nanowires have a bending angle Θ of 20° or less. At the points where these silver nanowires intersect, black circles 25 indicate intersections where the silver nanowires are in contact and have low electrical resistance, while white circles 26 indicate intersections where the silver nanowires are not in contact or, even if they are in contact, have high electrical resistance. In these cases, current does not flow easily, and the overall resistance of the electrodes is high.

[0018] Figure 2(B) is a conceptual diagram of a network 22 that includes silver nanowires 23A with a large bending angle. This network contains many silver nanowires 23 with a small bending angle Θ, but also includes silver nanowires 24 with a bending angle Θ of 90° or more. Due to this structure, there are relatively many intersections where silver nanowires come into contact with each other, resulting in a lower resistance value.

[0019] The minimum radius of curvature r and bending angle Θ were determined by observing a transparent electrode with a scanning electron microscope, using a field of view of 100 μm². 2The above field of view is determined by randomly selecting and evaluating three points. To perform the evaluation automatically, the observed images are binarized, and an AI is used to learn and recognize which is a single silver nanowire, and then the bending angle Θ and minimum radius of curvature are determined.

[0020] Generally, silver nanowires are often linear, and commonly known silver nanowire networks contain many silver nanowires with a small bending angle Θ, for example, silver nanowires 23 with a bending angle Θ of 20° or less. Silver nanowires that are closer to linear tend to have lower electrical resistance. Therefore, it is preferable to include many silver nanowires with a small bending angle. Specifically, it is preferable that the content of silver nanowires with a bending angle Θ of 20° or less, based on the number of silver nanowires included in the network, be 80% or more. However, when forming a network, compared to a network containing silver nanowires with a large bending angle, a network containing only silver nanowires with a small bending angle tends to have less contact between silver nanowires, and the overall electrical resistance of the network tends to be higher. In contrast to such a network containing only silver nanowires with a small bending angle, the network according to this embodiment, which includes silver nanowires 24 with a minimum radius of curvature r of the curve of 2 μm or less and a bending angle Θ of 90° or more, tends to have increased contact between silver nanowires and lower electrical resistance. Even if silver nanowires intersect, they are not necessarily in contact. Since the length of silver nanowires is finite, in order to allow current to flow from one end of the network to the other, it is necessary to increase the number of contact points between particularly close silver nanowires, and for this purpose, a network containing silver nanowires having the shape described above is preferable.

[0021] Silver nanowires are generally shorter than 100 μm, and it is difficult to form longer ones. When considering silver nanowires of such length, a radius of curvature of 2 μm or less tends to result in a higher number of contact points. Furthermore, a bending angle Θ of 90° or greater increases the opportunities for silver nanowires to intersect with other identical silver nanowires, leading to a higher number of low-resistance contact points. It should be noted that silver nanowires bend under stress, and the stress points often coincide with contact points with other silver nanowires. Therefore, a larger bending angle Θ indicates stronger contact between silver nanowires at those points, and also increases the number of contact points, thus reducing the overall electrical resistance of the network.

[0022] Silver nanowires with a large bending angle Θ are preferable because the number of contact points tends to increase further when the bending angle Θ is 120° or greater. This is because as the bending angle Θ increases, the number of intersections of the silver nanowires increases, as shown by the dashed line in Figure 2(B).

[0023] Furthermore, the number of contact points tends to increase as the number of silver nanowires with a large bending angle Θ increases. Specifically, when the content of silver nanowires with a bending angle Θ of 90° or more, based on the number of silver nanowires included in the network, is 1% or more, the number of contact points tends to increase. However, when it exceeds 5%, the electrical resistance tends to increase. This is thought to be because the highly bent silver nanowires themselves have many crystal defects, resulting in higher electrical resistance. From this perspective, the content of silver nanowires with a bending angle Θ of 90° or more is preferably 2-4%.

[0024] A silver nanowire with an average diameter of 20-50 nm is preferable because it tends to be flat and provides sufficient electrical conductivity. If it is smaller than 20 nm, the electrical resistance increases, and the length becomes insufficient, making it difficult to form a network. If it is larger than 50 nm, the surface irregularities increase and the dispersibility tends to worsen. The average diameter of the silver nanowire is preferably 30-40 nm.

[0025] A silver nanowire with an average length of 5-20 μm is preferable because it can form a network and reduce electrical resistance. If the average length of the silver nanowire is shorter than 5 μm, it becomes difficult to form a network, and electrical resistance tends to increase. If it is longer than 20 μm, dispersibility tends to worsen.

[0026] The efficiency of solar cells, organic EL elements, etc., can be increased if the sheet resistance of the transparent electrode, including the network, is 10 Ω / □ or less. However, if the sheet resistance is too low, the light transmittance tends to decrease. From this perspective, the sheet resistance of the transparent electrode is preferably 6 to 10 Ω / □.

[0027] The transparent electrode can impart conductivity between silver nanowires if it contains a conductive inorganic oxide, a conductive organic polymer, or graphene. This increases overall conductivity and improves efficiency. The conductive inorganic oxide can be arbitrarily selected from those used in the semiconductor field, such as ITO, AZO, and SnO2. These can be deposited by dry coating such as sputtering, or by wet coating using a nanoparticle dispersion.

[0028] As conductive organic polymers, polythiophene-based and polypyridine-based conductive polymers are preferred, and PEDOT-containing polymers are preferred.

[0029] In transparent electrodes, a graphene layer can also be laminated onto silver nanowires. The graphene layer is preferably one to four layers on average. Unsubstituted or nitrogen-doped graphene is preferred. Nitrogen-doped graphene is preferred for the cathode. The doping amount (N / C atomic ratio) can be measured by X-ray photoelectron spectroscopy (XPS), and is preferably 0.1 to 30 atom%, more preferably 1 to 10 atom%. The graphene film has a high shielding effect and can prevent metal microcluster.

[0030] It is preferable that the transparent electrode contains a compound having an alkynyl group and a hydroxyl group. The alkynyl group readily reacts with silver to form acetylides, and the hydroxyl group has high dispersibility in water and high adsorption through hydrogen bonding when dry. Due to these effects, this compound promotes bonding between silver nanowires (details below).

[0031] The transparent electrode according to the embodiment may be formed on a substrate. Examples of substrate materials include glass, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyvinyl chloride (PVC), polycarbonate (PC), polyvinylidene fluoride (PVDF), epoxy resin, acrylic resin, and silicone resin.

[0032] [Embodiment 2] The configuration of the transparent electrode according to the second embodiment will be explained using Figure 3. Figure 3 is a conceptual diagram of the transparent electrode 30 according to Embodiment 2.

[0033] This transparent electrode 30 has a network 32 composed of silver nanowires 31. Furthermore, this transparent electrode has a compound 33 having an alkynyl group 34 and a hydroxyl group 35, with a boiling point of 160°C or less. Compounds having alkynyl and hydroxyl groups readily react with silver to form acetylides due to their alkynyl groups. On the other hand, hydroxyl groups have high dispersibility in water and high adsorption due to hydrogen bonding when dry. As a result, the silver nanowires are easily bonded together by compound 33, and low-resistance contact points 36 are easily formed. Since the boiling point is 160°C or less, compounds that have not reacted with the silver nanowires during the manufacturing process can be easily removed by heating. Since compound 33, being an organic compound, is generally insulating, it is preferable to remove any compounds that do not participate in bonding between the silver nanowires.

[0034] Such compounds include, for example, the following formula (1): [ka] (R is a linear or branched hydrocarbon chain having 1 to 6 carbon atoms, which may be substituted with halogens, and n and m are independently 1 or 2.) A representation of this is preferable.

[0035] A specific example of the compound represented by formula (1) is 3,5-dimethyl-1-hexyn-3-ol. This compound also has surfactant properties, which improves the coating performance of silver nanowire dispersions. Furthermore, because the acetylene hydrogen and hydroxyl group are at the shortest possible distance from each other, it facilitates bonding between silver nanowires.

[0036] If the content of the compound represented by formula (1) in the transparent electrode is 1% by weight or less relative to the silver nanowire by mass, the bonding between the silver nanowires is strong, and at the same time, the electrical resistance can be reduced.

[0037] In the transparent electrode according to Embodiment 2, the silver nanowires are bonded by a compound having an alkynyl group and a hydroxyl group, resulting in high conductivity. However, if this compound is present during manufacturing, the bending angle of the silver nanowires increases during the manufacturing process of the transparent electrode, making it possible to obtain the transparent electrode of Embodiment 1.

[0038] [Embodiment 3] The manufacturing method for the transparent electrode 40 of Embodiment 3 will be explained using Figure 4. (A) A step of preparing a dispersion 43 containing silver nanowires 41 and a compound 42 having an alkynyl group and a hydroxyl group, (B) A step of preparing a precursor film 43A by coating the dispersion onto the substrate 44, and (C) A step of heating and drying the precursor film to produce a transparent electrode 40. It holds.

[0039] Step (A) is preferably performed immediately before step (B). This is because the dispersion may gel due to stagnation. The dispersion is prepared by dispersing silver nanowires and compound 42 in a dispersion medium. The boiling point of the dispersion medium is preferably low.

[0040] The silver nanowires can be selected from any conventionally known type, but it is preferable that the average diameter of the silver nanowires is 20 to 50 nm and the average length is 5 to 20 μm.

[0041] Compound 42 is, for example, the compound represented by formula (1) above. The boiling point of compound 42 can be 160°C or lower. This allows the drying temperature in step (C) to be lowered, so that substrates with low heat resistance, such as polymer substrates, can be used.

[0042] Furthermore, in the dispersion, it is preferable that the total mass of the compound is equal to or greater than the total mass of the silver nanowires. This improves the dispersibility of the silver nanowires.

[0043] Step (B) can be carried out by any conventionally known method. Specifically, these include spin coating, bar coating, slit coating, roller coating, dip coating, and curtain coating. Figure 4 shows the case of application using bar coating with bar 45.

[0044] After step (B), in step (C), excess dispersion medium and compound 42 are removed by heating and drying. The heating and drying conditions in step (C) are adjusted according to the dispersion medium, compound, etc. used. Preferably, the content of compound 42 in the transparent electrode obtained by heating and drying is 1% by mass or less, based on the total mass of the silver nanowire.

[0045] According to this method, the silver nanowires are bonded together by compound 42, increasing the bending angle of the silver nanowires, thus enabling the creation of the transparent electrode according to Embodiment 1.

[0046] [Embodiment 4-1] The configuration of a photoelectric conversion element according to one embodiment of the fourth electronic device will be explained using Figure 5. Figure 5 is a schematic diagram of the configuration of a solar cell 50 (photoelectric conversion element) according to this embodiment. The solar cell 50 is an element that functions as a solar cell, converting light energy such as sunlight L that is incident on the cell into electricity. The solar cell 50 comprises a photoelectric conversion layer 52 provided on the surface of a transparent electrode 51 and a counter electrode 53 provided on the opposite side of the transparent electrode 51 of the photoelectric conversion layer 52. Here, the transparent electrode 51 is the same as that shown in Embodiment 1 or 2.

[0047] The photoelectric conversion layer 52 is a semiconductor layer that converts the light energy of incident light into electricity to generate an electric current. Generally, the photoelectric conversion layer 52 comprises a p-type semiconductor layer and an n-type semiconductor layer. As the photoelectric conversion layer, a laminate of a p-type polymer and an n-type material, RNH3PbX3 (where X is a halogen ion, R is an alkyl group, etc., and may also contain alkali metal ions), silicon semiconductors, inorganic compound semiconductors (e.g., InGaAs, GaAs, chalcopyrite-based, CdTe-based, InP-based, SiGe-based, Cu2O-based, etc.), quantum dot-containing semiconductors, and even dye-sensitized transparent semiconductors may be used. In any case, high efficiency can be achieved and output degradation can be reduced.

[0048] A buffer layer may be inserted between the photoelectric conversion layer 52 and the transparent electrode 51 to promote or block charge injection.

[0049] The counter electrode 53 is usually an opaque metal electrode, but a transparent electrode according to the embodiment may also be used. Another charge buffer layer or charge transport layer may be inserted between the counter electrode 53 and the photoelectric conversion layer 52.

[0050] As the buffer layer and charge transport layer for the anode, for example, layers composed of PEDOT / PSS, p-type polymers, 2,2’,7,7’-Tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9’-spirobifluorene (hereinafter referred to as Spiro-OMeTAD), vanadium pentoxide (V2O5), nickel oxide (NiO), tungsten trioxide (WO3), molybdenum trioxide (MoO3), etc. can be used. The ratio of metal to oxygen in the oxide does not necessarily have to be a stoichiometric ratio.

[0051] On the other hand, as the buffer layer and charge transport layer for the transparent electrode serving as the cathode, layers composed of lithium fluoride (LiF), calcium (Ca), 6,6’-phenyl-C 61 -methyl butyrate (6,6’-phenyl-C 61 -butyric acid methyl ester, hereinafter referred to as C 60 -PCBM), 6,6’-phenyl-C 71 -methyl butyrate (6,6’-phenyl-C 71 -butyric acid methyl ester, C 70 -PCBM), indene-C 60 bisadduct (Indene-C 60 bisadduct, ICBA), cesium carbonate (Cs2CO3), titanium dioxide (TiO2), poly[(9,9-bis(3’-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctyl-fluorene)] (PFN), bathocuproine (BCP), zirconium oxide (ZrO), zinc oxide (ZnO), cerium oxide (CeO2), polyethyleneimine, etc. can be used. The ratio of metal to oxygen in the oxide does not necessarily have to be a stoichiometric ratio.

[0052] For the counter electrode 53, an electrode having the same structure as the transparent electrode 51 may be used. Alternatively, the counter electrode 53 may contain unsubstituted planar single-layer graphene. Unsubstituted single-layer graphene can be produced by a CVD method using methane, hydrogen, and argon as reaction gases and copper foil as the underlying catalyst layer. For example, after pressing a thermal transfer film and a single-layer graphene together, the copper is dissolved and the single-layer graphene is transferred onto the thermal transfer film. By repeating the same operation, multiple single-layer graphenes can be laminated on the thermal transfer film, and 2 to 4 graphene layers can be produced. By printing metal wiring for current collection on this film using silver paste or the like, it can be used as a counter electrode. Alternatively, instead of unsubstituted graphene, graphene in which some carbon is replaced with boron may be used. Boron-substituted graphene can be produced similarly using BH3, methane, hydrogen, and argon as reaction gases. After forming these graphenes on a thermal transfer film, they can also be transferred onto a suitable substrate such as PET.

[0053] These single-layer or multi-layer graphenes may also be doped with tertiary amines as electron donor molecules. Electrodes made of such graphene films can also function as transparent electrodes.

[0054] The solar cell according to this embodiment can have a structure in which both sides are sandwiched between transparent electrodes. Solar cells having such a structure can efficiently utilize light from both sides. The energy conversion efficiency is generally 5% or more, and it is characterized by being stable and flexible over a long period of time.

[0055] Furthermore, instead of a graphene film, an ITO glass transparent electrode can be used as the counter electrode 53. In this case, the flexibility of the solar cell is sacrificed, but light energy can be utilized with high efficiency. Alternatively, stainless steel, copper, titanium, nickel, chromium, tungsten, gold, silver, molybdenum, tin, zinc, etc. may be used as the metal electrode. In this case, transparency tends to decrease.

[0056] Solar cells can have an ultraviolet-blocking layer and a gas barrier layer. Specific examples of ultraviolet absorbers include: Benzophenone compounds such as 2-hydroxy-4-methoxybenzophenone, 2,2-dihydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxy-2-carboxybenzophenone, and 2-hydroxy-4-n-octoxybenzophenone; Benzotriazole compounds such as 2-(2-hydroxy-3,5-di-3-butylphenyl)benzotriazole, 2-(2-hydroxy-5-methylphenyl)benzotriazole, and 2-(2-hydroxy-5-3-octylphenyl)benzotriazole; Salicylic acid ester compounds such as phenylsalicylate and p-octylphenylsalicylate These include [mention specific examples]. It is desirable that these cut out ultraviolet light below 400nm.

[0057] The gas barrier layer is preferably one that blocks water vapor and oxygen, and is especially preferably one that is impermeable to water vapor. For example, Si3N4, SiO2, SiC, SiO x N y Layers made of inorganic materials such as TiO2 and Al2O3, and ultrathin glass sheets can be suitably used. The thickness of the gas barrier layer is not particularly limited, but it is preferably in the range of 0.01 to 3000 μm, and more preferably in the range of 0.1 to 100 μm. Below 0.01 μm, sufficient gas barrier properties tend not to be obtained, while above 3000 μm, it tends to become heavy and lose features such as flexibility and pliability. The water vapor permeability (moisture transmission) of the gas barrier layer is 100 g / m². 2 ·d~10 -6 g / m 2 • d is preferred, more preferably 10 g / m 2 ·d~10 -5 g / m 2 • d, and more preferably 1 g / m 2 ·d~10 -4 g / m 2·d. Furthermore, moisture permeability can be measured according to JIS Z0208, etc. Dry methods are preferred for forming a gas barrier layer. Methods for forming a gas barrier layer using dry methods include vacuum deposition methods such as resistance heating deposition, electron beam deposition, induction heating deposition, and methods assisted by plasma or ion beams, sputtering methods such as reactive sputtering, ion beam sputtering, and ECR (electron cyclotron) sputtering, physical vapor deposition (PVD) methods such as ion plating, and chemical vapor deposition (CVD) methods using heat, light, plasma, etc. Among these, vacuum deposition, which forms a film by deposition under vacuum, is preferred.

[0058] When the transparent electrode according to the embodiment includes a substrate, the type of substrate is selected according to the purpose. For example, as the transparent substrate, inorganic materials such as glass, or organic materials such as PET, PEN, polycarbonate, PMMA, polyvinyl chloride, and PVDF can be used. In particular, using a flexible organic material is preferable because it makes the transparent electrode according to the embodiment highly flexible.

[0059] Furthermore, the solar cell of this embodiment can also be used as a light sensor.

[0060] [Embodiment 4-2] The configuration of a photoelectric conversion element according to a fourth embodiment will be described using Figure 6. Figure 6 is a schematic diagram of the configuration of an organic EL element 60 (photoelectric conversion element) according to this embodiment. The organic EL element 60 is an element that functions as a light-emitting element that converts electrical energy input to the element into light L. The organic EL element 60 comprises a photoelectric conversion layer (light-emitting layer) 62 provided on the surface of a transparent electrode 41 and a counter electrode 63 provided on the opposite side of the transparent electrode 61 of the photoelectric conversion layer 62.

[0061] Here, the transparent electrode 61 is the same as that shown in Embodiment 1 or 2. The photoelectric conversion layer 62 is an organic thin film layer that recombines the charge injected from the transparent electrode 61 with the charge injected from the counter electrode 63 to convert electrical energy into light. The photoelectric conversion layer 62 usually consists of a p-type semiconductor layer and an n-type semiconductor layer. A buffer layer is provided between the photoelectric conversion layer 62 and the counter electrode 63 to promote or block charge injection, and another buffer layer may be provided between the photoelectric conversion layer 62 and the transparent electrode 51. The counter electrode 63 is usually a metal electrode, but a transparent electrode may be used.

[0062] (Example 1) A transparent electrode with the structure shown by surface SEM in Figure 7 was fabricated. A PET film with a thickness of 125 μm was coated with an aqueous dispersion containing 0.3 wt% silver nanowires with an average diameter of 30 nm and an average length of 5 μm, and 0.35 wt% 3,5-dimethyl-1-hexyn-3-ol. The film was then heated and dried at 120°C to create a silver nanowire layer. The resulting film had a sheet resistance of 6 Ω.

[0063] This transparent electrode has a silver nanowire content of 92% based on the number of nanowires with a bending angle of 20° or less, and a silver nanowire content of 1.9% based on the number of nanowires with a minimum curvature radius r of 2 μm or less and a bending angle Θ of 90° or more (the total number of nanowires measured was 465). Figure 8 shows a cross-sectional SEM image. It can be seen that the silver nanowires are in close proximity to each other.

[0064] When this transparent electrode is heated at 150°C for 10 minutes, the resulting gas is collected, separated by ion chromatography, and analyzed by mass spectrometry, a small amount of 3,5-dimethyl-1-hexyn-3-ol is detected.

[0065] (Comparative Example 1) A transparent electrode was prepared in the same manner as in Example 1, except that 3,5-dimethyl-1-hexyn-3-ol was not added. Figure 9 shows the surface SEM. Most of the silver nanowires had a bending angle of 20° or less, and no silver nanowires with a minimum radius of curvature r of 2 μm or less and a bending angle Θ of 90° or more were observed. The sheet resistance of this transparent electrode was 9 Ω, which is higher than that of Example 1. Figure 10 shows the cross-sectional SEM. It can be seen that the silver nanowires are more spaced apart compared to Example 1.

[0066] (Example 2) A PET film with a thickness of 125 μm was meniscus-coated with an aqueous dispersion containing 0.2 wt% silver nanowires with an average diameter of 30 nm and an average length of 5 μm, and 0.25 wt% 3,5-dimethyl-1-hexyn-3-ol. The dispersion was then heated and dried at 120°C to produce a silver nanowire layer. The resulting film had a sheet resistance of 13 Ω.

[0067] This transparent electrode has a silver nanowire content of 84% based on the number of nanowires with a bending angle of 20° or less, and a silver nanowire content of 2.3% based on the number of nanowires with a minimum radius of curvature r of 2 μm or less and a bending angle Θ of 90° or more.

[0068] (Example 3) A PET film with a thickness of 125 μm was meniscus-coated with an aqueous dispersion containing 0.3 wt% silver nanowires with an average diameter of 30 nm and an average length of 5 μm, and 0.3 wt% 3,5-dimethyl-1-hexyn-3-ol. The dispersion was then heated and dried at 120°C to produce a silver nanowire layer. The resulting film had a sheet resistance of 7 Ω.

[0069] This transparent electrode has a silver nanowire content of 89% based on the number of nanowires with a bending angle of 20° or less, and a silver nanowire content of 1.4% based on the number of nanowires with a minimum radius of curvature r of 2 μm or less and a bending angle Θ of 90° or more.

[0070] (Example 4) A solar cell 110, as shown in Figure 11, is fabricated.

[0071] A pH 6.0 aqueous dispersion of neutral PEDOT (CleviosPJet) is meniscus-coated onto the transparent electrode 111 obtained in Example 1, and then heated to create a PEDOT layer 112.

[0072] Poly(3-hexylthiophene-2,5-diyl) and C 60 -A chlorobenzene solution containing PCBM is applied to the meniscus and dried at 100°C for 20 minutes to produce a photoelectric conversion layer 113. Next, C 60 -A toluene solution of PCBM is applied as a meniscus and dried to create an electron transport layer 114. Next, an aqueous solution of lithium fluoride is applied as an electron injection layer 115. Aluminum is deposited on top of that to create a counter electrode 116.

[0073] A UV-blocking layer 117 is fabricated by screen printing a UV-blocking ink containing 2-hydroxy-4-methoxybenzophenone onto the surface of a transparent substrate. A silica film is then deposited on the UV-blocking layer using a vacuum deposition method to create a gas barrier layer 118, and the entire structure is sealed with a film to produce a solar cell 110.

[0074] The resulting solar cells exhibit an energy conversion efficiency of 5% or more for 1 sun's worth of sunlight.

[0075] (Example 5) The solar cell 120 shown in Figure 12 is fabricated.

[0076] An AZO nanoparticle dispersion is applied to the transparent electrode 121 obtained in Example 1 and heated to create an AZO layer 122. An isopropanol solution of tetraisopropoxytitanium is applied on top of this and heated to create an electron injection layer 123 consisting of a TiOx layer. The TiOx may deviate from the stoichiometric weight and may contain alkyl groups. Next, an isopropanol solution of PbI2 is applied. Next, an isopropanol solution of methylammonium iodide is applied. A photoelectric conversion layer 124 is created by drying at 100°C for 10 minutes. Next, a toluene solution of Spiro-OMeTAD is applied and heated to create a hole transport layer 125. An ITO film is sputtered on top of this to create a counter electrode 126.

[0077] A UV-blocking layer 127 is fabricated by screen printing a UV-blocking ink containing 2-hydroxy-4-methoxybenzophenone onto the surface of a transparent substrate. A silica film is then deposited on the UV-blocking layer by vacuum deposition to create a gas barrier layer 128, thereby fabricating a translucent solar cell 120.

[0078] The resulting solar cells exhibit an energy conversion efficiency of 10% or more for 1 sun's worth of sunlight.

[0079] (Example 6) An organic EL device is fabricated. An AZO nanoparticle dispersion is applied to the transparent electrode obtained in Example 1 and heated to create an AZO layer. An aqueous solution of lithium fluoride is applied as an electron injection layer, and tris(8-hydroxyquinoline)aluminum (Alq3) (40 nm), which functions as both an n-type semiconductor and an emissive layer, is deposited to create a photoelectric conversion layer. On top of that, N,N'-di-1-naphthyl-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (NPD) is deposited to a thickness of 30 nm to create a hole transport layer. A gold electrode is then deposited on top of that by sputtering. Finally, the surrounding area is sealed to fabricate an organic EL device. The resulting organic EL device has an efficiency of 20% or more. [Explanation of Symbols]

[0080] 10... Silver nanowires 11...Current 21…Transparent substrate 22…Network 23. Silver nanowires with a bending angle Θ of 20° or less 24...Silver nanowires with a minimum radius of curvature r of 2 μm or less and a bending angle Θ of 90° or more 25… Intersections with low electrical resistance 26… Intersections with high electrical resistance 30…Transparent electrode 31... Silver nanowires 32…Network 33...Compound 34...Alkynyl group 35...Hydroxyl group 40...Transparent electrode 41…Silver nanowires 42...Compound 43...Dispersion liquid 43A… Precursor film 44... Circuit board 45... Bar 40…Organic EL elements 41...Transparent electrode 42…Photoelectric conversion layer 43… Counter electrode 50… Solar cells 51...Transparent electrode 52…Photoelectric conversion layer 53... Counter electrode 60…Organic EL elements 61...Transparent electrode 62... Photoelectric conversion layer 63... Counter electrode 64...Electron injection layer 65... Opposite electrode 110… Solar cell 111...Transparent electrode 112…PEDOT layer 113... Photoelectric conversion layer 114...Electron transport layer 115...Electron injection layer 116... Counter electrode 117… UV-blocking layer 118... Gas barrier layer 120… Solar cell 121...Transparent electrode 122...AZO layer 123...electron injection layer 124... Photoelectric conversion layer 125... Hole transport layer 126... Counter electrode 127… UV-blocking layer 128... Gas barrier layer

Claims

1. A transparent electrode having a network of silver nanowires, wherein the network includes curved silver nanowires having a minimum radius of curvature r of 2 μm or less and a bending angle Θ of 120° or more, and the content of curved silver nanowires with a bending angle Θ of 90° or more, based on the number of silver nanowires included in the network, is 1% or more, and the content of silver nanowires with a bending angle Θ of 20° or less, based on the number of silver nanowires included in the network, is 80% or more. Here, the bending angle Θ of the silver nanowire is the maximum value of the angle between the vector directions of any two points in the silver nanowire, when a current flows through the silver nanowire in a constant direction. (Transparent electrode)

2. The transparent electrode according to claim 1, wherein the average diameter of the silver nanowires included in the network is 20 to 50 nm.

3. The transparent electrode according to claim 1 or 2, wherein the average length of the silver nanowires included in the network is 5 to 20 μm.

4. A transparent electrode according to claim 1 or 2, wherein the sheet resistance is 10 Ω / □ or less.

5. A transparent electrode according to claim 1 or 2, further comprising a conductive inorganic oxide, a conductive organic polymer, or graphene.

6. The transparent electrode according to claim 1 or 2, further comprising a compound having an alkynyl group and a hydroxyl group.

7. The transparent electrode according to claim 1 or 2, further comprising a compound having a boiling point of 160°C or lower and having an alkynyl group and a hydroxyl group.

8. The transparent electrode according to claim 7, wherein the compound is 3,5-dimethyl-1-hexyn-3-ol.

9. The transparent electrode according to claim 7, wherein the content of the compound is 1% by mass or less, based on the total mass of the silver nanowires included in the network.

10. The transparent electrode according to claim 7, further comprising a conductive inorganic oxide, a conductive organic polymer, or graphene.

11. (A) A step of producing a dispersion containing curved silver nanowires and a compound having an alkynyl group and a hydroxyl group. (B) A step of applying the dispersion onto a substrate, and (C) A process of heating and drying the substrate after coating. A method for manufacturing a transparent electrode according to claim 1 or 2, comprising having

12. The method according to claim 11, wherein the boiling point of the compound is 160°C or lower.

13. The method for manufacturing a transparent electrode according to claim 11, wherein the average diameter of the silver nanowires is 20 to 50 nm.

14. The method for manufacturing a transparent electrode according to claim 11, wherein the average length of the silver nanowire is 5 to 20 μm.

15. The method for producing a transparent electrode according to claim 11, wherein in the dispersion of step (A), the total mass of the compound is equal to or greater than the total mass of the silver nanowires.

16. An electronic device comprising a transparent electrode according to claim 1 or 2, a photoelectric conversion layer, and a counter electrode on a transparent substrate.

17. The electronic device according to claim 16, wherein the counter electrode is transparent.

18. The electronic device according to claim 16, wherein the photoelectric conversion layer contains halogen ions.

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